The introduction of luminescent semiconductor nanocrystals or quantum dots (QDs) to biology has provided researchers with novel fluorescent tools for potentially achieving advances in imaging and sensing. See, for example, U.S. Patent Application Publication Nos. 2008/0087843 and 2011/0089241, each of which is incorporated herein by reference. This arises from the unique photophysical properties that these fluorophores provide including: size-tunable narrow, symmetrical photoluminescence (PL, full-width at half-maximum ˜25-40 nm) and broad absorption spectra that increase towards shorter wavelengths. Using different semiconductor materials it is possible to prepare nanocrystals with emissions ranging from the UV to the near infrared region of the optical spectrum. QDs also exhibit high quantum yields, a pronounced resistance to chemical degradation, and high photo-bleaching thresholds. A particularly useful property is that multiple QDs present in the same sample can be efficiently excited at a single wavelength far removed (>100 nm) from their respective emissions. This makes QDs directly amenable to signal multiplexing, i.e., the simultaneous detection of multiple concurrent fluorescent emissions or channels.
A need exists to control photophysical properties of quantum dots.